Machines, including wheel loaders, motor graders, and other types of heavy machinery generally include a multi-speed, bidirectional, mechanical transmission drivingly coupled to an engine by way of a torque converter assembly. The torque converter is a fluid coupling that multiplies and/or absorbs torque fluctuations transmitted between the engine and the traction devices of the machine by allowing slippage between an output shaft of the engine and an input shaft of the transmission. The torque converter assembly includes an impeller clutch to allow the operator a degree of freedom in determining the slippage between the output shaft of the engine and the input shaft of the torque converter (i.e., the impeller). The impeller clutch allows for high engine speeds while limiting the amount of torque that is transmitted into the torque converter, thus allowing some of the torque to be directed for other purposes.
As an operator depresses an impeller clutch pedal, the force keeping the impeller clutch engaged is proportionally reduced. As the force decreases, the clutch may begin to slip and less torque is transmitted from the engine to the torque converter. The amount of force applied to the clutch is selected such that, when the clutch pedal is depressed, the torque generated by the engine is modulated for only one machine application condition, such as digging, as it is passed to the torque converter.
Although efficient for applications requiring high torque, the modulation of the force applied to the clutch as the pedal is depressed may be sub-optimal during applications that require low torque, such as truck loading. That is, during applications requiring high torque, such as digging, the clutch pedal offers a higher resolution for operator control. However, due to the preset modulation for higher torque, modulation of the transmitted torque is not refined enough for applications requiring low torque.
One system focused on improved torque transfer during different operations is disclosed in U.S. Pat. No. 5,720,358 (the '358 patent) issued to Christensen et al. on Feb. 24, 1998. The '358 patent discloses an electric control device for a drive train of a machine including an engine, a transmission, a torque converter, and an impeller clutch. A manually operated impeller clutch pedal produces an impeller clutch pedal signal in response to the position of the impeller clutch pedal. An impeller clutch electro-hydraulic valve produces fluid flow to the impeller clutch to controllably engage and disengage the impeller clutch. An impeller clutch pressure curve that is responsive to the impeller clutch pedal position is stored in memory, where an electronic controller selects an impeller clutch engine speed. An electronic controller can also determine if a machine is digging. An electronic controller receives the signal that the machine is digging and selects a desired torque converter engine speed. The torque converter engine speed is a desired engine speed that corresponds to a desired maximum torque. This allows the machine to control the maximum torque during digging conditions. Further, the electronic controller modulates the torque through receiving signals based on pressures from the hydraulic cylinders, speed from the torque converter, and speed of the engine
Although the device of the '358 patent may improve control over the impeller clutch, it may still be sub-optimal. That is, the control over the engine speed is only for digging applications. The system still has some delays associated with operation of the machine during applications that require different amounts of torque and slip. As such, the modulation of the torque during different applications is not sufficiently refined.
The disclosed control system is directed to one or more improvements in the existing technology.